1. Field of the Invention
The present invention relates to a digital signal processing apparatus and a digital signal processing method. Particularly, it relates to the digital signal processing apparatus and method for processing an input digital image signal and generating an output digital image signal.
2. Description of the related art
Recently, an image display device using a cathode-ray tube as a display device has been connected with a variety of digital devices to display an image on the display device. On the image display device, the resolution has been also enhanced so that the image display device can display an image very finely. Therefore, when a signal output from the digital device is a SD (Standard Definition) signal corresponding to a video signal according to NTSC system the SD signal may be converted into a HED (High Definition) signal corresponding to a video signal with a high resolution to display an image of high quality and thus converted signal may be supplied to the image display device.
Moreover, as the display device, not only a cathode-ray tube has been used, but also a liquid crystal display panel, plasma display panel or the like has been used for reducing the power consumption, upsizing the display screen, reducing the space and so forth.
When types of display devices are different, for example, if a SD signal is converted into a HD signal and thus converted signal is supplied to the image display device having display device such as liquid crystal display panel, as do the image display device using the cathode-ray tube, this may prevent such image display device having liquid crystal display panel from displaying an image of high quality because of the difference of the characteristics of display devices.
FIGS. 1 and 2 respectively show the characteristics of a cathode-ray tube and a liquid crystal display element used as a display device. Now, in the case of a cathode-ray tube, as shown in FIG. 1, it is known that the relationship between an input signal and a luminance changes in proportion to an input signal to the power of xcex3(=about 2.2). On the other hand, in the case of a liquid crystal display element, as to the relationship between the input signal and the light transparency (luminance), when a signal level of input signal is low or high, the changing amount of the luminance is little, as shown in FIG. 4. Further, when the signal level is at intermediate level, the luminance largely changes corresponding to a signal level of the input signal. Therefore, for example, when the input signal is in a range of A or Axe2x80x2, no changes of the input signal appear as the difference of luminance, and thus its luminance information is missed in the liquid crystal display element. Moreover, in the liquid crystal display element, since strengths of electric field applying to a liquid crystal layer are different depending upon dispersion of a liquid crystal cell in the direction of thickness thereof, a dispersion of the luminance may occur. Furthermore, the contrast ratio in a liquid crystal display element is in the order of a fraction of that of the cathode-ray tube. Therefore, where a liquid crystal display element is used as a display device, a high quality display image may be obtained by making up the deficit tone rather than by enhancing the resolution.
It is accordingly an object of the invention to provide digital signal processing apparatus and method capable of displaying an image of a high quality by enhancing the resolution or by making up the tone corresponding to a display device for use.
The present invention relates to a digital signal processing apparatus comprising generating means for generating an output digital image signal and control means for controlling the generating means. According to his invention, the generating means is supplied with an input digital image signal. In accordance with one aspect of the invention, a plurality of pixel data adjacent to a subject pixel data is selected out of the input digital image signal and clustered to produce each class. A memory stores predictive operation parameter data for respective classes at addresses corresponding to the respective classes determined by the clustering means. Selecting means selects a plurality of pixel data corresponding to a pixel data of the output digital image signal from the input digital image signal. Predictive operating means operates said predictive operation parameter data from said memory and the plurality of pixel data from said selecting means. The control means controls the generating means such that the generating means selects one of a plurality of kinds of predictive operation and generates the output digital image signal corresponding to the selected kind of predictive operation.
In accordance with another aspect of the invention, a digital signal processing method for processing an input digital image signal and generating an output digital image signal is provided. In the method, a plurality of pixel data of the input digital image signal adjacent to a subject pixel data are clustered to produce each class, and predictive operation parameter data for respective classes is stored at addresses of memory corresponding to the respective classes determined by the clustering means. A plurality of pixel data are then selected from the input digital image signal corresponding to a pixel data of the output digital image signal. The predictive operation parameter data from the memory and the plurality of pixel data from said selecting means are operated to produce a plurality of kinds of predictive operation of generating means. Further, one of the kinds of predictive operation is selected to generate the output digital image signal corresponding to the selected kind of predictive operation.
The conclusion portion of this specification particularly points out and distinctly claims the subject matte of the present invention. However those skill in the art will best understand both the organization and method of operation of the invention, together with further advantages and objects thereof, by reading the remaining portions of the specification in view of the accompanying drawing(s) wherein like reference characters refers to like elements.